This invention relates to a process for producing transparent elastomeric polymer films particularly suitable for wrapping heat-sensitive articles, to the transparent elastomeric films themselves, and to articles wrapped in such films.
Transparent films are commonly used for packaging various consumer items, which thus can be examined by the prospective purchaser without opening the package. The most common are heat-shrinkable films, but those cannot be used for packaging heat-sensitive products, especially certain food articles. There are also used non-elastomeric stretch-films, such, for example, as poly(vinylidene chloride). Those films, however, lack sufficient elastic recovery for forming an esthetically pleasing, snug overwrap.
Certain ethylene/vinyl acetate copolymers (sometimes hereafter abbreviated to EVA copolymers), especially those containing about 30-50 weight % of vinyl acetate comonomer, form a transparent elastomeric film, which can be used in packaging applications. In order to improve the film's formability, for example, creep resistance, the film is normally exposed to high energy radiation, which induces crosslinking. But even though such irradiated EVA copolymer films having a vinyl acetate content in excess of 30% have satisfactory mechanical properties, they also have high surface tackiness, which causes difficulties both in production windup and in machine packaging applications.
Various approaches to solving this high tackiness problem have been proposed. For example, the copending application Ser. No. 259,422 of Mahr et al. filed May 1, 1981, now U.S. Pat. No. 4,310,212, proposes alcoholysis or hydrolysis of surface vinyl acetate groups, preferably followed by attachment to the surface of finely divided mineral particulates. Another copending application of Mahr et al., Ser. No. 278,435, filed June 25, 1981, now U.S. Pat. No. 4,374,898, teaches treating the EVA film surface with a coupling agent and then attaching particulate material to the surface.
However, still other methods of improving the properties and reducing the surface tackiness of elastomeric EVA films are sought.